Why is dict definition faster in Python 2.7 than in Python 3.x?

I have encountered a (not very unusual) situation in which I had to either use a

map()

or a list comprehension expression. And then I wondered which one is faster.

This StackOverflow answer provided me the solution, but then I started to test it myself. Basically the results were the same, but I found an unexpected behavior when switching to Python 3 that I got curious about, and namely:

I had the assumption that Python 3 is faster than Python 2, but it turned out in several posts (1, 2) that it's not the case. Then I thought that maybe Python 3.5 will perform better at such a simple task, as they state in their

README

:

The language is mostly the same, but many details, especially how
built-in objects like dictionaries and strings work, have changed
considerably, and a lot of deprecated features have finally been
removed.

, but my knowledge of C language is not sufficient to find the answer myself (or, maybe I even don't search in the right place).

So, my question is:

What makes the newer version of Python slower comparing to an older version of Python on a relatively simple task such as a

dict

definition, as by the common sense it should be vice-versa? I'm aware of the fact that these differences are so small that in most cases they can be neglected. It was just an observation that made me curious about why the time increased and not remained the same at least?